CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.

I use 9mm RP primed brass for hot loads and do not re use them

That was with a ~ 1990's Kel-Tec P11 9mm pistol that has been slightly throated to take a 158 gr .358" LSWC at 1.169" over all length. The loaded ammo is resized to fall into and out of the chamber. Otherwise, the bullet will pinch and the primer will pierce at 8 gr in the work up. There is so much powder compressed in there, that the bullet and case become bulged. Resizing the loaded ammo makes the cartridge withing size specifications. The carbide ring in a Lee factory crimp is larger than a sizing and is designed for this, but any sizing die works, if used judiciously.

The main things I look for to determine a starting load in a work up for a semi auto pistol is case support and chamber wall thickness.

I just measured 8 different 9mm pistol designs and the chamber wall thickness varies between .980" for a Beretta FS and 1.360" for a Star Super-B.

The Kel-tec P11 has chamber walls at .105"

Someone with a Dillon loaded me a large quantity of 10 gr Power Pistol 124 gr flat point. Shooting this from the Kel-Tec chronographs at 1336 fps and the recoil really hurts. But in one of the Beretta 92 pistols, with heavy slide and wide frame grip, there is no recoil pain.

I have measured the case support in various 9mm pistols that vary from .145" to .190", with .190" being the most common.

The web of a 9mm cartridge case head is .160" thick, leaving .030" of thin unsupported case wall in the .190" support barrels. But the case wall is ~ .015" thick, so it is not a long span, compared to some pistols sold as 40sw, 10mm, or 45acp.

I speculate that lawyered up risk averse corporations would copy the 9mm example and offer +P+ ammo for 40sw, 10mm, and 45acp if no pistols were manufactured with more than .030" of thin case wall left unsupported.